This investigation is designed to provide information about the role of the arterial smooth muscle cell in atherosclerosis. Pigtail monkeys (macaca nemestrina) will be utilized for correlative in vitro and in vivo biochemical and morphological studies of three events that clearly are important features of the disease: 1. smooth muscle cell proliferation, 2. connective tissue formation by smooth muscle, and 3. lipid accumulation by smooth muscle. The effects of plasma growth factors including platelet derived factors and lipoproteins on these events will be studied in vitro utilizing cell cultures of arterial smooth muscle derived from the media of the aorta and standardized with respect to such factors as age and sex of the donor, composition of the medium, and phase of cell growth. Complementary experiments will be performed concamitantly in vivo by selectively removing the endothelium of the iliac artery and abdominal aorta with a balloon catheter and following the development of the resulting lesion. This lesion is characterized by the accumulation of smooth muscle cells and connective tissue components in the intima and is similar in appearance to the early atherosclerosis plaque. The possibility that deendothelialization promotes the development of the lesion by removing a barrier to plasma and platelet growth factors and lipoproteins will be tested by following smooth muscle proliferation, connective tissue protein formation, and lipid accumulation as functions of changes in arterial wall permeability that accompany the removal and subsequent regrowth of the endothelium.